Organometallic fragments in microporous solids: intrazeolite chemistry of (cyclooctatetraene)iron tricarbonyl

Abstract

The intrazeolite reactivity of (COT)Fe(CO)3 (COT = cyclooctatetraene) [ 11 in faujasites having different levels of Bronsted acidity was examined with extended X-ray absorption fine structure, vibrational, and temperature programmed desorption/mass spectrometric techniques. The data show that the precursor complex [ l ] associates with Na-Y zeolite, resulting in symmetry changes of the Fe(C0)3 fragment while 1 remains chemically intact. If (COT)Fe(CO)3 is adsorbed into highly acidic H-Y zeolite at room temperature, bicyclo[5.1 .O]octadienyliron tricarbonyl cation is formed in a clean reaction. This reaction corresponds to the protonation of 1 with noncoordinating acids in homogeneous solution. At elevated temperatures, the carbonyl ligands are cleaved off and the remaining organo-iron fragment is anchored to framework oxygens of the large zeolite supercages. IntroductionMany organometallic complexes have successfully been used in homogeneous catalysis. Often these catalyst systems are highly selective and allow mild reaction conditions to be used. However, difficult separation of the catalyst from the products or deactivation due to irreversible structural changes can compromise the benefits of homogeneous catalytic systems. In an attempt to combine the advantages of both homogeneous and heterogeneous systems, molecular catalysts have in the past been supported on various metal oxides. A wide range of transition-metal s-allyl, cyclopentadienyl (Cp), carbonyl, and olefin derived catalyst precursors have been prepared during the past decade, including group IV, VI, and VI11 metal species supported on amorphous oxides. '-5 In contrast to classical amorphous catalyst supports, the crystalline pore structure of zeolites offers a unique potential to control substrate access through diffusional selectivity and to modify catalytic transition states. The present study is part of a research program aimed at the synthesis of well-defined, stable hybrid catalysts by anchoring transition-metal species into zeolite supports. We explore the reactivity of transition-metal complexes in acid forms of zeolites. Anchoring of metal species into the zeolite cavities can in principle be achieved by substituting leaving groups at the transition-metal complex with zeolite oxygen. As a basis for the rational design of zeolite-based hybrid catalysts, we study the different relative reactivities and stabilities of ligands at a metal center with respect to the bridged intrazeolite hydroxyls (ZOH). In this study, the intrazeolite reactivities of cyclooctatetraene (COT) and carbonyl ligands of (COT)Fe(C0)3 [ 11 have been examined.The protonation of (COT)Fe(C0)3 in homogeneous solution has been well studied. Key reactions are summarized in Scheme

A Mononuclear Cyclopentadiene–Iron Complex Grafted in the Supercages of HY Zeolite: Synthesis, Structure, and Reactivity

“…[18] It is worth noting that similar intrazeolite transformations have been proposed to yield half-sandwich organometallic fragments by the reactions of [(cot)Fe(CO) 3 ] (cot = cyclooctatriene) and [{CpFe(CO) 2 } 2 ] with acid zeolites. [19] These investigations suggested the need for a study to better understand the chemical nature of these so-called half-sandwich organometallic complexes inside a zeolite.…”

Intrazeolite organometallics and coordination complexes: internal versus external confinement of metal guests

“…Another recently reported example concerns the intrazeolite reactivity of (COT)Fe(CO)3 in NaY. 34 The IR data of the carbonyl bands provide evidence for interactions of the type Na+-OC(CO)2Fe(COT), which resembles contact ion-pair interactions of carbonyl complexes with alkali-metal cations in solution.33 In the case of intrazeolite dicobalt octacarbonyl the IR stretching frequency of the bridging carbonyls decreases by about 30 cm'1 while the terminal bands increase in frequency by 10-15 cm'1 relative to the silica-supported material. Preferential cation interaction with bridging carbonyls is observed in solution and results in similar frequency shifts.…”

Sorption Sites, Energetics, and Reactions of Molybdenum Hexacarbonyl and Benzene Cosorbed in Faujasitic Zeolites

“…In choosing the archetypical reaction between Mo(CO) 6 and benzene, the following criteria should be satisfied: (i) the reaction has been well studied in homogeneous solutions; (ii) the intrazeolite benzene is structurally and spectroscopically well documented in FAU, Na 56 FAU, and Na 85 FAU, − respectively. In addition, the mobility of benzene in FAU and Na 56 FAU has been recently studied by molecular dynamics calculations; − (iii) pertinent knowledge to the characterization of the intrazeolite Mo(CO) 6 and Mo(CO) 3 species as well as dynamic motions has been acquired to date. − …”

“…In addition, the mobility of benzene in FAU and Na 56 FAU has been recently studied by molecular dynamics calculations; 20-24 (iii) pertinent knowledge to the characterization of the intrazeolite Mo(CO) 6 and Mo-(CO) 3 species as well as dynamic motions has been acquired to date. [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] Techniques utilized to date to investigate the metal carbonyl species encapsulated in zeolites include chemical techniques, IR, Raman, ESR, NMR, XPS, EXAFS spectroscopy. However, many of these techniques are particularly devoted to highly loaded samples.…”